It is a routine requirement of a variety of surgical procedures to utilize extracorporeal cardiopulmonary bypass in order to mechanically perform the functions normally conducted by the heart and lungs. Venous blood depleted in oxygen and rich in carbon dioxide is removed from the patient and pumped to an oxygenating apparatus in order to oxygenate the blood and remove excess carbon dioxide. The blood is then returned to the patient's arterial system.
It is important that adequate volumes of blood be drained from the patient during cardiopulmonary bypass so that the extracorporeal life support equipment can keep up with the patient's need for oxygen and can adequately remove excess carbon dioxide. Insufficient quantities of oxygen can lead to serious tissue damage. Inadequate removal of carbon dioxide leads to a condition known as “acidosis,” which can result in serious consequences caused by the alternation in normal metabolic functioning of critical enzymes. Either condition can result in serious injury to the patient.
A general technique involves using a drainage cannula to remove the venous blood from the patient for extracorporeal treatment. Such cannulae can have drainage openings at the distal end and also along their length proximal to the distal end. Such cannulae are inserted through the right atrium and extend into either the inferior vena cava or the superior vena cava or both, with the proximal drainage openings positioned within the right atrium. This placement permits blood to be drained simultaneously from the right atrium and from surrounding vena cavae.
Surgically placed cannulae are frequently used in various surgical procedures, such as, but not limited to the procedure described above, to draw blood from or introduce blood into patient vessels. In some cases there is a need for a cannula to have holes in the sidewall to allow blood flow through the sidewall during procedures. In cannulae, such as drainage cannulae, that have a sidewall made from a coiled spring, the holes along the length of the cannula can be formed by cutting the spring and placing a solid-walled tube between the two cut ends. Holes can then be punched into the solid-walled section of the cannula. However, this type of cannula design results in a weakness of the cannula in the area that has no spring, and the cannula can separate at the joints between the spring and solid-walled tube during use.